KATMANDU, Nepal — Bikash Suwal, a lithe, tanned Nepali trekking guide, has climbed the 18,805-foot Yala Peak in the towering Himalayas. But since a powerful earthquake rocked Nepal a week ago, he has been afraid to climb the stairs to the rented rooms he shares with five family members.

Like many of his neighbors in the usually thrumming Gongabu area of Katmandu, Mr. Suwal fears that the buildings still standing are so poorly constructed that they may be toppled by aftershocks.

“A mountain is safer than this,” he said Wednesday of the four-story concrete and brick building where he lives. “Up there, climbing, I sometimes feel afraid, but not like this. This kind of danger is not in my hands.”

Jittery fear has coursed through Nepal’s storied capital, Katmandu, since Saturday’s quake, which is thought to have killed more than 6,250 people across Nepal. Ancient temples in Katmandu crumpled from the intense pulses of seismic energy that the earthquake unleashed, but so did many dozens of buildings constructed after a modern building code was put in place.

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Houses on a hillside north of Katmandu, seen from an Indian Army helicopter, were destroyed in last week’s earthquake.CreditDaniel Berehulak for The New York Times

That has ignited public alarm that the collapses exposed not only flaky concrete and brittle pillars, but also a system of government enforcement rotted by corruption and indifference.

Residents and building experts say the corruption is an open secret, as evident as the unlicensed five- and six-story buildings that have risen in recent years, displacing two-story ones that sprang up in former farm fields starting a decade or so ago. The developers and landlords who slap up the buildings, the residents and experts say, know they will rarely be punished by officials, who are often happy to look the other way for a price.

“We pay like this,” said Bir Bahadur Khadwada — the owner of the Kalika Guesthouse, frequented by migrant workers in Gongabu — as he rubbed his thumb with his index finger under his dining table. “They go away.”

Nepali experts said bribery, lax law enforcement and a lack of land-use controls left buildings vulnerable to seismic disasters. But several said those problems were symptoms of a deeper failing: the government’s inability to keep up with a rapidly urbanizing society.

Since the nation’s building code was introduced in the 1990s, the population of greater Katmandu more than doubled. It grew to 1.74 million in 2011, the year of the last census, from 675,000 in 1991 as migrants began pressing into the city, drawn by jobs and services that distant villages can only dream about: regular electricity, water and satellite television.

In recent decades, however, the Nepali government has undergone a convulsive succession of crises, including a bloody 10-year civil war with Maoist insurgents, that diverted government priorities and revenue from the task of managing urban growth.

Geology further complicated matters: Katmandu is the ancient bed of a lake, and haphazard urban growth has allowed construction to spread to risky terrain, said Richard Sharpe, a New Zealand earthquake engineer who helped draft Nepal’s building code. “You shouldn’t just go and build anywhere,” he said. “You’ve got very soft soils in some places.”

Despite many such warnings from scientists in recent years, modern housing, malls and shops, some built with breathless haste, filled in the contours of a city revered for its ancient monuments and temples.

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Nepali soldiers helped residents clear their belongings from damaged homes in Shankarapur on Friday.CreditDaniel Berehulak for The New York Times

“I think there’s still a hell of a lot of informal building,” Mr. Sharpe said in a telephone interview, referring to unlicensed and unplanned development. “And you’re in the Katmandu Valley, but what about the other 90 percent of the people, who are in the hills? How can you enforce the building code in the hills?”

The tally of the damage in those villages remains incomplete, with many isolated from rescuers by landslides and severed roads. In central Katmandu, at least 175 residential buildings were destroyed, according to satellite images compiled and assessed by the European Commission’s Copernicus Emergency Management Service. The Nepali authorities estimate that nationwide, nearly 150,000 dwellings collapsed. But larger, modern buildings, including urban hospitals and schools, mostly withstood the earthquake, reflecting more robust construction.

Nepal’s building code set what experts call admirable standards, but officials often enforced it in a perfunctory way, despite experts’ warnings that the country was in a region where a giant earthquake was a real risk, said Niyam Maharjan, a building engineer who works for the country’s Ministry of Federal Affairs and Local Development.

“It’s too late,” he said this week, “but they are listening to us now.”

The effects of Katmandu’s uncontrolled growth are distilled in Gongabu, where dozens of buildings collapsed and others slipped off their foundations and onto their sides.

The neighborhood has grown helter-skelter in recent years into an enclave for poorer workers, tourists and people abandoning the mountains for the city. Its identity is so caught up in Katmandu’s wild expansion that it is nicknamed New Bus Park, for the neighborhood’s long-distance bus terminal, where many migrants first arrive.

The area is a maze of four-, five- and six-story buildings — mainly shops, guesthouses that cater to poor Nepalis traveling to and from Katmandu for work and business, and small apartment buildings, often with small shops on their ground floors. Residents said bribery to allow illegal construction was common, and land-use planning unheard-of.

“The buildings are taller and taller, but they want to save money on making them,” said Sumah Thapa, a stocky 30-year-old who makes a living selling tickets at the nearby bus station.

When the earthquake struck on Saturday, residents rushed onto the main street to escape the swaying buildings. But many did not make it. Officials would not say how many people in the area had died, though residents offered estimates ranging from dozens to hundreds.

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The Boudhanath Stupa, center, one of the oldest Buddhist monuments in the Himalayas, four days after the earthquake.CreditManish Swarup/Associated Press

Residents checked off the particular sins, saying regulations on building height and construction materials were regularly ignored, as were specifications for safety features like pillars.

“Fourteen years ago, it was fields of vegetables, barley, potatoes,” said Jit Bahadur Limbu, a shop owner and longtime resident. “But now, even if our government doesn’t give permission, people make five- to seven-story buildings.”

He added, “The builder or your engineer pays the inspector to not make trouble and then gives you the bill.”

He and other residents estimated that bribes ranged from a few dollars to a few hundred, depending on the size of the project. Mr. Khadwada, the guesthouse owner, said that several years ago, through his building contractor, he had paid inspectors about $150 so they would turn a blind eye to two extra floors built on top of his guesthouse, in addition to the two permitted by construction codes.

Days after the earthquake, many residents of New Bus Park remained in tents outside their homes and scoffed at the government’s suggestion that most houses in Katmandu were safe enough for them to move back indoors at night.

“I’m still scared,” said Mr. Suwal, the trekking guide. “We will have to move back into our homes, but maybe the house is too weak for the next time. Can they tell us?”

Gardiner Harris contributed reporting from New Delhi.

A version of this article appears in print on , on Page A4 of the New York edition with the headline: Nepal’s Fast Urbanization and Lax Enforcement Add to Quake’s Toll. Order Reprints | Today’s Paper | Subscribe